1. Field of the Invention
The present invention relates to plasma display devices, and more particularly, to device and method for operating a plasma display panel.
2. Background of the Related Art
In general, the plasma display panel (hereafter called as “PDP”) makes fluorescent material to emit a light by using a UV beam emitted when an inert gas, such as He+Xe, Ne+Xe, or He+Xe+Ne, discharges, for displaying a picture. The PDP is, not only easy to fabricate a thin and large sized device, but also under improvement of a picture quality owing to recent development of technologies.
Referring to FIG. 1, a unit discharge cell of the PDP is provided with a scan electrode Y and a common sustain electrode Z formed in parallel under an upper substrate 10, and an address electrode X on the lower substrate 18. The scan electrode Y is provided with a transparent electrode Ya and a metal bus electrode Yb having a width smaller than the transparent electrode Ya, and the common sustain electrode Z is provided with a transparent electrode Za and a metal bus electrode Zb having a width smaller than the transparent electrode Za. The transparent electrodes Ya and Za are in general formed of Indium-Tin-Oxide (ITO), and the metal bus electrodes Yb and Zb are in general formed of a metal such as chrome, each for reducing a voltage drop caused by the transparent electrode Ya or Za.
There are an upper dielectric layer 14 and a protection film 16 stacked on the upper substrate 10. The upper dielectric layer 14 accumulates wall charges generated at the time of plasma discharge, and the protection film 16 prevents the upper dielectric layer 14 suffering from damage occurred at the time of the plasma discharge, and enhances a discharge efficiency of secondary electrons. The protection film 16 is in general formed of magnesium oxide MgO.
There are a lower dielectric layer 22 and a barrier 24 on the lower substrate 18 having the address electrode X formed thereon, and a fluorescent material layer 26 is coated on surfaces of the lower dielectric layer 22 and the barrier 24. The address electrode X is formed to cross the scan electrode Y and the common sustain electrode Z. The barrier 24 is formed parallel to the address electrode X for prevention of leakage of the UV ray and visible light emitted by discharge to adjoining discharge cells. The fluorescent material layer 26 emits one of red, green and blue visible light by the UV ray emitted at the time of the plasma discharge.
For making the PDP to display gray levels of the picture, one frame is time divided into sub-fields each having different number of light emission times. The sub-field has a reset period for resetting an entire screen, an address period for selecting a scan line and selecting a cell on the selected scan line, and a sustain period for displaying a gray level according to the number of discharge times.
In the address period, a scan pulse is provided to the scan electrode Y, and a data pulse is provided to the address electrode X in synchronization to the scan pulse. In this instance, an address discharge is occurred at the discharge cell having the scan pulse and the data pulse provided thereto. After the scan pulse is provided to all the scan electrodes Y, the sustain pulse is provided to the scan electrode Y and the common sustain electrode Z alternately. Thereafter, sustain discharges are occurred at the discharge cells at which the address discharges are occurred.
For an example, referring to FIG. 3, if it is intended to display the picture with 256 gray levels, a frame period (16.67 ms= 1/60 second) is divided into 8 sub-fields SF1˜SF8. As described, each of the 8 sub-fields SF1˜SF8 has the reset period, the address period, and the sustain period. Though the reset periods, and the address periods are identical between the sub-fields, a number of the sustain pulses assigned to the sustain period increases in a rate of 2n (n=0, 1, 2, 3, 4, 5, 6, and 7).
Referring to FIG. 2, since the related art PDP is operated by single scan method in which the scan electrode lines Y1˜Yn are scanned one by one in succession, the related art PDP requires a long address period. Consequently, since it is required to reduce a time period allocated to the sustain period following the address period, a high luminance is not available from the PDP. For solving the problems, a dual scan method rises, in which the scan electrode lines are divided into upper scan electrode lines and lower scan electrode lines, equally.
However, the related art dual scan method has a problem in that the PDP causes high temperature mis-discharge at a high temperature. As shown in FIG. 4, the high temperature mis-discharge is a phenomenon in which some of the cells ‘A’ are turned off when the PDP is operated at a high environmental temperature in a range of 50˜70° C. The cells are turned off mostly in a central part because the high temperature mis-discharge is distinctive as time goes by after a set up discharge in a case the scan is directed toward the central part.
A major reason of the high temperature mis-discharge is failure of the address discharge caused by loss of wall charge during the address period. The wall charge loss during the address period is caused in the following two cases, mostly. First, insulating property of the protection film (MgO) and the dielectric layer becomes weak as inside and outside temperatures of the discharge cell 1 rise, to cause the wall charge leakage, particularly at the scan electrode Y and the sustain electrode Z. Second, when the PDP is at a high temperature, movements of spatial charges in the discharge cell become active such that re-bonding of the charges is vulnerable to cause a loss of the wall charges.